JP2010256634A - Image forming apparatus and control method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which reduces errors of respective A/D converters due to a difference of reference potential in a plurality of CPUs without increasing cost in distributed control using the plurality of CPUs. <P>SOLUTION: The image forming apparatus achieves the distributed control using the plurality of CPUs. The image forming apparatus calculates a difference of digital data output from the respective A/D converters in such a state that a switch is controlled so that output from the same surface electrometer may be input in the A/D converters in a correction mode. Furthermore, the image forming apparatus corrects output from the A/D converters so that the difference calculated in the correction mode may be canceled in an ordinary measurement mode. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus realized by a distributed control system having a plurality of CPU groups having a hierarchical structure.

  In printer device control of an image forming apparatus that employs an electrophotographic system, centralized control is performed by one CPU. However, a CPU with higher performance is required due to an increase in CPU load due to a single point of control. Further, as the control load of the printer device increases, it is necessary to route the communication cable (communication bundle) to the control load driver unit that is separated from the CPU board, and many long communication cables are required. In order to solve such a problem, a control form in which each control module constituting the electrophotographic system is divided into individual sub CPUs has attracted attention.

  Examples of constructing a control system by dividing individual partial module control functions by a plurality of CPUs as described above have been proposed in some control device product fields other than copying machines. For example, Patent Document 1 proposes a technique in which functional modules in a vehicle are arranged hierarchically to perform distributed control. For example, when it is attempted to realize distributed control in an image forming apparatus that performs color image formation, it is conceivable to provide a plurality of control units that respectively control a plurality of engines that perform image formation for each color. Each control unit includes an A / D converter that performs A / D conversion on an output from a sensor that detects the state of each engine (for example, the surface potential of the photosensitive drum). Here, a reference power source is connected to each A / D converter provided in each control unit. These reference power supplies are designed to have the same voltage among a plurality of A / D converters.

JP 2000-120490 A

  In reality, however, there are individual differences in the reference power supply and A / D converter and the influence of the ambient temperature. Therefore, even if each sensor outputs the same value, a different value is used in each A / D converter. May be converted to Patent Document 1 proposes a technique for eliminating analog data transmission errors by referring to the reference potential of the D / A converter of the master controller and A / D converting the A / D converter of the slave controller. Yes. However, when the technique disclosed in Patent Document 1 is applied to the image forming apparatus, even if the reference potential can be corrected with reference to the reference potential of another control unit, the same as the other control unit There is no guarantee that the value can be A / D converted.

  The present invention has been made in view of the above-described problems. In distributed control using a plurality of CPUs, an error of each A / D converter due to a difference in reference potentials in each CPU without causing an increase in cost. An object of the present invention is to provide an image forming apparatus that reduces the above-described problem.

  The present invention can be realized as an image forming apparatus, for example. An image forming apparatus includes a plurality of output units that output analog data, a plurality of analog-digital converters that are connected to any of the output units and convert analog data into digital data, and an output unit and the analog-digital converter. At least one switching unit that is provided in between and switches the output unit to which the analog-digital converter is connected, and the switching unit is controlled so that the output from the same output unit is input to each analog-digital converter And a correction unit for correcting the output from each analog-digital converter in order to eliminate the difference between the digital data output from each analog-digital converter.

  The present invention can provide, for example, an image forming apparatus that reduces an error of each A / D converter due to a difference in reference potential in each CPU without causing an increase in cost in distributed control using a plurality of CPUs.

1 is a diagram illustrating an overview of an image forming apparatus 1000 according to a first embodiment. FIG. 3 is a cross-sectional view illustrating a configuration example of an image forming unit 300 according to the first embodiment. It is a figure which shows typically the relationship of the master CPU which concerns on 1st Embodiment, a submaster CPU, and a slave CPU. 2 is a diagram illustrating an example of a control board of the image forming apparatus 1000 according to the first embodiment. FIG. It is a figure which shows the structural example of the image creation module 282 which concerns on 1st Embodiment. It is a block diagram which shows the connection condition of submaster CPU701, slave CPU702, and slave CPU704 which concern on 1st Embodiment. 6 is a flowchart showing a part of the processing procedure of the image forming module 282 according to the first embodiment. It is a figure which shows the modification of the correction data which concerns on 1st Embodiment. It is a block diagram which shows the connection condition of submaster CPU701, slave CPU702, and slave CPU704 which concern on 2nd Embodiment. 10 is a flowchart showing a part of the processing procedure of the image forming module 282 according to the second embodiment. It is a figure which shows the relationship between the apparatus internal temperature and A / D value which concern on 2nd Embodiment.

  Hereinafter, the first embodiment will be described with reference to FIGS. 1 to 8. FIG. 1 shows an overview of an image forming apparatus 1000 according to the first embodiment. The image forming apparatus 1000 includes an automatic document feeder 100, an image reading unit 200, an image forming unit 300, and an operation unit 10. As shown in FIG. 1, the image reading unit 200 is placed on the image forming unit 300. Further, an automatic document feeder (DF) 100 is placed on the image reading unit 200. Further, the image forming apparatus 1000 implements distributed control using a plurality of control units (CPUs). The configuration of each CPU will be described later with reference to FIG.

  The automatic document feeder 100 automatically conveys a document onto a platen glass. The image reading unit 200 reads a document conveyed from the automatic document conveying device 100 and outputs image data. The image forming unit 300 forms an image on a recording material in accordance with image data output from the automatic document feeder 100 or image data input from an external device connected via a network. The operation unit 10 has a GUI (graphical user interface) for a user to perform various operations. Furthermore, the operation unit 10 includes a display unit such as a touch panel, and can present information to the user.

  Next, the details of the image forming unit 300 will be described with reference to FIG. Note that the image forming unit 300 of the present embodiment employs an electrophotographic system. Note that alphabets Y, M, C, and K shown at the end of the reference numbers in FIG. 2 indicate engines corresponding to yellow, magenta, cyan, and black toners, respectively. In the following, when referring to engines corresponding to all toners, the reference letters are described by omitting the alphabets Y, M, C, and K at the end, and alphabets Y, M, and C are added at the end of the reference numerals when indicated individually. , K is added and described.

  A photosensitive drum (hereinafter simply referred to as “photosensitive member”) 225 for forming a full-color electrostatic image as an image carrier is provided to be rotatable in the direction of arrow A by a motor. Around the photoconductor 225, a primary charging device 221, an exposure device 218, a developing device 223, a transfer device 220, a cleaner device 222, a charge eliminating device 271 and a surface potential meter 273 are arranged.

  The developing device 223K is a developing device for monochrome development, and develops the latent image on the photoreceptor 225K with K toner. The developing devices 223Y, M, and C are developing devices for full-color development, and the developing devices 223Y, M, and C develop latent images on the photoreceptors 225Y, M, and C with Y, M, and C toners, respectively. To do. The toner images of the respective colors developed on the photosensitive member 225 are collectively transferred onto the transfer belt 226 that is an intermediate transfer member by the transfer device 220, and the four color toner images are superimposed.

  The transfer belt 226 is stretched around rollers 227, 228, and 229. The roller 227 functions as a driving roller that is coupled to a driving source and drives the transfer belt 226, and the roller 228 functions as a tension roller that adjusts the tension of the transfer belt 226. The roller 229 functions as a backup roller for the transfer roller as the secondary transfer device 231. The transfer roller attaching / detaching unit 250 is a drive unit for adhering or releasing the secondary transfer device 231 to or from the transfer belt 226. A cleaner blade 232 is provided below the transfer belt 226 after passing through the secondary transfer device 231, and residual toner on the transfer belt 226 is scraped off by the blade.

  The recording materials (recording paper) stored in the cassettes 240 and 241 and the manual paper feed unit 253 are transferred to the nip portion, that is, the secondary transfer device 231 by the registration roller 255, the paper feed roller pair 235, and the vertical pass roller pairs 236 and 237. It is fed to the contact portion with the belt 226. At this time, the secondary transfer device 231 is in contact with the transfer belt 226 by the transfer roller attaching / detaching unit 250. The toner image formed on the transfer belt 226 is transferred onto the recording material at this nip portion. Thereafter, the recording material onto which the toner image has been transferred is thermally fixed by the fixing device 234 and discharged outside the device.

  The cassettes 240 and 241 and the manual sheet feeder 253 include sheet-less detection sensors 243, 244, and 245 for detecting the presence or absence of a recording material, respectively. The cassettes 240 and 241 and the manual paper feed unit 253 include paper feed sensors 247, 248, and 249 for detecting a pickup failure of the recording material, respectively.

  Here, an image forming operation by the image forming unit 300 will be described. When image formation is started, the recording materials stored in the cassettes 240 and 241 and the manual paper feed unit 253 are conveyed to the paper feed roller pair 235 one by one by the pickup rollers 238, 239 and 254. When the recording material is conveyed to the registration roller 255 by the pair of paper feed rollers 235, the registration sensor 256 immediately before the recording material detects passage of the recording material.

  In this embodiment, when the registration sensor 256 detects the passage of the recording material, the conveying operation is interrupted once after a predetermined time has elapsed. As a result, the recording material abuts against the stopped registration roller 255, and the conveyance is stopped. At this time, the conveyance position is fixed so that the traveling direction end of the recording material is perpendicular to the conveyance path. The skew of the state in which the transport direction is shifted with respect to the transport path is corrected. Hereinafter, this process is referred to as position correction. The position correction is necessary to minimize the inclination of the image forming direction with respect to subsequent recording materials. After the position correction, the recording material is supplied to the secondary transfer device 231 by starting the registration roller 255. The registration roller 255 is coupled to a driving source and is driven to rotate by being transmitted by a clutch.

  Next, a voltage is applied to the primary charging device 221 to uniformly negatively charge the surface of the photoconductor 225 at a predetermined charged portion potential. Subsequently, exposure is performed by an exposure device 218 including a laser scanner unit so that an image portion on the charged photoconductor 225 has a predetermined exposure unit potential, and a latent image is formed. The exposure device 218 forms a latent image corresponding to the image by turning on and off the laser beam based on the image data sent from the controller 460 via the printer control I / F 215. The surface potential meter 273 measures the surface potential of the photoconductor 225 whose surface is uniformly charged by the primary charging device 221 and outputs the measured surface potential.

  Further, a developing bias set in advance for each color is applied to the developing roller of the developing device 223, and the latent image is developed with toner when passing through the position of the developing roller, and visualized as a toner image. . The toner image is transferred to the transfer belt 226 by the transfer device 220, and further transferred to the recording material conveyed from the paper feeding unit by the secondary transfer device 231, and then passes through the post-registration conveyance path 268, and then the fixing conveyance belt. The sheet is conveyed to the fixing device 234 via 230.

  In the fixing device 234, the toner image is first fixed by the pre-fixing chargers 251 and 252 and the toner image is thermally fixed by the fixing roller 233 in order to compensate for the toner adsorption force and prevent the image disturbance. Thereafter, the recording material is discharged as it is onto the discharge tray 242 by the discharge roller 270 when the transport path is switched to the discharge path 258 side by the discharge flapper 257.

  The toner remaining on the photoreceptor 225 is removed and collected by the cleaner device 222. Finally, the photosensitive member 225 is uniformly discharged to near 0 volts by the discharging device 271 to prepare for the next image forming cycle.

  Since the color image formation start timing by the image forming apparatus 1000 is simultaneous transfer of Y, M, C, and K, it is possible to form an image at an arbitrary position on the transfer belt 226. However, it is necessary to determine the image formation start timing while shifting the shift of the position where the toner images on the photoconductors 225Y, M, and C are transferred in a timing manner.

  In the image forming unit 300, the recording material can be continuously fed from the cassettes 240 and 241 and the manual paper feeding unit 253. In this case, in consideration of the sheet length of the preceding recording material, paper is fed from the cassettes 240 and 241 and the manual paper feeding unit 253 at the shortest intervals so that the recording materials do not overlap. As described above, by activating the registration roller 255 after position correction, the recording material is supplied to the secondary transfer device 231. When the recording material reaches the secondary transfer device 231, the registration roller 255 is temporarily stopped again. . This is because position correction is performed on the subsequent recording material in the same manner as the preceding recording material.

  Next, the operation when an image is formed on the back surface of the recording material will be described in detail. When an image is formed on the back surface of the recording material, image formation on the surface of the recording material is first performed in advance. In the case of image formation only on the front surface, the toner image is thermally fixed by the fixing device 234 and then discharged to the discharge tray 242 as it is. On the other hand, when image formation on the back surface is continued, when the recording material is detected by the sensor 269, the conveyance path is switched to the back surface path 259 side by the paper discharge flapper 257, and the recording material is rotated by the rotation driving of the reverse roller 260 in conjunction therewith. Is conveyed to the double-side reversal path 261. Thereafter, the recording material is conveyed to the double-sided reversing path 261 by the width in the feeding direction, and then the traveling direction is switched by the reverse rotation driving of the reversing roller 260, and the double-sided path conveyance is performed with the image surface formed on the surface facing downward. The roller 262 is driven and conveyed to the duplex path 263.

  Subsequently, when the recording material is conveyed through the double-sided path 263 toward the paper re-feed roller 264, passage of the recording material is detected by the paper re-feed sensor 265 immediately before the recording material. When the re-feed sensor 265 detects the passage of the recording material, in this embodiment, the conveying operation is interrupted after a predetermined time has elapsed. As a result, the recording material abuts against the re-feed roller 264 that is stopped, and the conveyance is temporarily stopped. At this time, the position of the recording material is fixed so that the end portion in the traveling direction of the recording material is perpendicular to the conveyance path. The skew in which the recording material conveyance direction deviates from the conveyance path in the refeed path is corrected. Hereinafter, this process is referred to as reposition correction.

  The reposition correction is necessary to minimize the inclination of the image forming direction with respect to the back surface of the recording material thereafter. After the reposition correction, the re-feed roller 264 is activated, so that the recording material is conveyed again onto the paper feed path 266 with the front and back sides reversed. The subsequent image forming operation is the same as the above-described surface image forming operation, and is therefore omitted here. The recording material on which images are formed on both the front and back sides in this way is discharged to the discharge tray 242 by switching the transport path from the discharge flapper 257 to the discharge path 258 side.

  Note that the image forming unit 300 can continuously feed the recording material even during duplex printing. However, since there is only one system for forming an image on a recording material and fixing a formed toner image, printing on the front surface and printing on the back surface cannot be performed simultaneously. Therefore, at the time of duplex printing, the recording material from the cassettes 240 and 241 and the manual paper feeding unit 253 and the recording material that is reversed and fed to the image forming unit again for back side printing are printed on the image forming unit 300. Are alternately formed.

  The image forming unit 300 divides each control load shown in FIG. 2 into four control blocks, which will be described later, a conveyance module A 280, a conveyance module B 281, an image forming module 282, and a fixing module 283. Yes. Furthermore, a master module 284 for controlling these four control blocks to function as an image forming apparatus is provided. Hereinafter, the control configuration of each module will be described with reference to FIG.

  FIG. 3 is a diagram schematically showing a relationship among the master CPU, the sub-master CPU, and the slave CPU according to the first embodiment. In this embodiment, a master CPU (master control unit / first layer control unit) 1001 provided in the master module 284 is based on an instruction and image data sent from the controller 460 via the printer control I / F 215. The whole 1000 is controlled. Further, a transport module A 280, a transport module B 281, an image forming module 282, and a fixing module 283 for performing image formation are sub-master CPUs (sub master control units / second layer control units) 601 and 901 that control each function. 701 and 801 are provided. The sub master CPUs 601, 901, 701 and 801 are controlled by the master CPU 1001. Furthermore, each function module further includes slave CPUs (slave control units / third layer control units) 602, 603, 604, 605, 902, 903, 702, for operating a control load for executing each function. 703, 704, 705, 706, 802, 803. The slave CPUs 602, 603, 604, and 605 are controlled by the sub-master CPU 601, the slave CPUs 902 and 903 are controlled by the sub-master CPU 901, the slave CPUs 702, 703, 704, 705, and 706 are controlled by the sub-master CPU 701, and the slave CPUs 802 and 803 are controlled by the sub-master CPU 801.

  As shown in FIG. 3, the master CPU 1001 and the plurality of sub-master CPUs 601, 701, 801, 901 are bus-connected by a common network type communication bus (first signal line) 1002. The sub-master CPUs 601, 701, 801, and 901 are also bus-connected by a network type communication bus (first signal line) 1002. Note that the master CPU 1001 and the plurality of sub-master CPUs 601, 701, 801, and 901 may be ring-connected. The sub-master CPU 601 is further connected to each of the plurality of slave CPUs 602, 603, 604, 605 via a high-speed serial communication bus (second signal line) 612, 613, 614, 615 (peer-to-peer connection). Yes. Similarly, the sub-master CPU 701 is connected to slave CPUs 702, 703, 704, 705, and 706 via high-speed serial communication buses (second signal lines) 711, 712, 713, 714, and 715, respectively. The sub master CPU 801 is connected to slave CPUs 802 and 803 via high-speed serial communication buses (second signal lines) 808 and 809, respectively. The sub master CPU 901 is connected to slave CPUs 902 and 903 via high-speed serial communication buses (second signal lines) 909 and 910, respectively. Here, the high-speed serial communication bus is used for short-distance high-speed communication.

  In the image forming apparatus 1000 according to the present embodiment, control that requires responsiveness depending on timing is divided into functions so as to be realized in a functional module integrated with each sub-master CPU. Therefore, communication between each slave CPU and each sub-master CPU for driving the terminal control load is connected by a high-speed serial communication bus with good responsiveness. In other words, a signal line with higher data transfer timing accuracy than the first signal line is used for the second signal line.

  On the other hand, between the sub-master CPUs 601, 701, 801, 901 and the master CPU 1001, only exchanges that control the rough processing flow of the image forming operation without requiring precise control timing are performed. For example, the master CPU 1001 instructs the sub-master CPU to start pre-image formation processing, start paper feed, and start post-image formation processing. Further, the master CPU 1001 issues an instruction based on a mode (for example, a monochrome mode or a double-sided image formation mode) designated by the controller 460 to the sub-master CPU before starting image formation. Only exchanges that do not require precise timing control are performed between the sub-master CPUs 601, 701, 801, and 901. That is, the control of the image forming apparatus is divided into control units that do not require precise timing control, and each sub-master CPU controls each control unit at precise timing. As a result, in the image forming apparatus 1000, communication traffic can be minimized and connection can be made with a low-speed and inexpensive network-type communication bus 1002. Note that the master CPU, the sub-master CPU, and the slave CPU are not necessarily required to have a uniform control board, and can be variably arranged according to the circumstances in mounting the apparatus.

  Next, a specific arrangement of the master CPU, the sub master CPU, and the slave CPU in the present embodiment on the board configuration will be described with reference to FIG. According to the present embodiment, various control board configurations can be employed as shown in FIG. For example, the sub master CPU 601 and the slave CPUs 602, 603, 604, 605 are mounted on the same substrate. Further, like the sub master CPU 701 and the slave CPUs 702, 703, and 704, or the sub master CPU 801 and the slave CPUs 802 and 803, the sub master CPU and each slave CPU may be mounted as independent boards. Also, some slave CPUs such as slave CPUs 705 and 706 may be mounted on the same substrate. Further, like the sub master CPU 901 and the slave CPU 902, only a part of the sub master CPU and the slave CPU may be arranged on the same substrate.

  FIG. 5 shows a configuration example of the image forming module 282 according to the first embodiment. The image forming module 282 controls image formation until the full-color toner image formed by the electrophotographic process is transferred to the transfer belt 226 and further retransferred to the recording material delivered from the transport module A280. The image forming module 282 includes a sub master CPU 701 that comprehensively controls image forming control, and slave CPUs 702, 703, 704, 705, and 706 that drive each control load. In addition, a control load group that is directly controlled is connected to each slave CPU.

  The slave CPU 702 uses the exposure device 218K, the developing device 223K, the primary charging device 221K, the transfer device 220K, the cleaner device 222K, and the charge removal device 271K as control loads, and performs control until the black toner image is transferred to the transfer belt 226. Do. The slave CPU 703 uses the exposure device 218M, the developing device 223M, the primary charging device 221M, the transfer device 220M, the cleaner device 222M, and the charge eliminating device 271M as control loads, and performs control until the magenta toner image is transferred to the transfer belt 226. Do. The slave CPU 704 uses the exposure device 218C, the developing device 223C, the primary charging device 221C, the transfer device 220C, the cleaner device 222C, and the charge removal device 271C as control loads, and performs control until the cyan toner image is transferred to the transfer belt 226. Do. The slave CPU 705 performs control until the cyan toner image is transferred to the transfer belt 226 using the exposure device 218Y, the developing device 223Y, the primary charging device 221Y, the transfer device 220Y, the cleaner device 222Y, and the charge eliminating device 271C as control loads. .

  The slave CPU 706 controls the motor 708 of the roller 227 that drives the transfer belt 226 to rotate, the high-voltage signal output device that drives the secondary transfer device 231, the transfer roller attaching / detaching unit 250, and the drive source motors 709 and 710 that drive the registration rollers. And Further, the slave CPU 706 controls these control loads and performs control until the secondary transfer device 231 re-transfers the four-color toner image transferred onto the transfer belt 226 onto the recording material. In this embodiment, the sub-master CPU 701 and the slave CPUs 702, 703, 704, 705, and 706 are connected to each other in a one-to-one relationship by independent high-speed serial communication buses 711, 712, 713, 714, and 715.

  Next, with reference to FIG. 6, a configuration characteristic of the present embodiment of the sub-master CPU 701, the slave CPU 702, and the slave CPU 704 in the image forming module 282 will be described. The DC / DC converters 272K and 272Y output predetermined output voltages / currents and supply power to the boards of the slave CPUs 702 and 704, respectively. The surface potential meters 273K and 273Y are an example of an output unit, and measure and output the drum surface potentials of the photoconductors 225K and 225Y uniformly charged by the primary charging device 221. A / D converters (analog / digital converters) 276K and 276Y are provided in the slave CPU 702 and the slave CPU 704, respectively, and convert analog data into digital data. The switch 274 is an example of a switching unit. For example, as illustrated in FIG. 6, the switch 274 is provided between the surface electrometers 273K and 273Y and the A / D converter 276Y, and selects two inputs for A / D conversion. To the device 276Y.

  As described above, in the image forming module 282, the slave CPUs 702 and 704 are supplied with power from the DC / DC converters 272K and 272Y, respectively. These reference potentials are preferably completely the same in order to reduce the output error of the A / D converters 276K and 276Y provided on each substrate, but the circuit design and the ambient temperature at which the substrate is provided Because of their characteristics, they are never completely the same. Therefore, for example, when measuring the drum surface potential of the photoreceptors 225K and 225Y using the A / D converters 276K and 276Y connected to the surface potentiometers 273K and 273Y, a difference occurs in each A / D converter. As a result, the image quality is degraded. Therefore, in this embodiment, the error of each A / D converter due to the difference in the reference potential is eliminated by the configuration and processing described below.

  First, the connection status of each element will be described. Vcc (24V) is connected to the input of DC / DC converters 272Y, 272K. The output of the DC / DC converter 272K is connected to the ref input of the A / D converter 276K. The output of the DC / DC converter 272Y is connected to the ref input of the A / D converter 276Y. The output of the surface electrometer 273K is connected to the input of the A / D converter 276K via the signal line 716 and to one input of the switch 274. The output of the surface electrometer 273Y is connected to the other input of the switch 274 via the signal line 717. The output of the switch 274 is connected to the input of the A / D converter 276Y via a signal line 718. That is, the switch 274 switches the output destination of the surface potential input to the A / D converter 276Y.

  Next, control for creating correction data for A / D values output from the A / D converter in the configuration of FIG. 6 will be described with reference to FIG. The processing described below is centrally controlled by the sub-master CPU 701, slave CPU 702, and slave CPU 704 in the image forming module 282. The numbers starting with S described below indicate step numbers in the flowchart.

  First, in S101, the sub-master CPU 701 instructs the slave CPU 704 to select the signal line 716 for the input of the switch 274 at the timing before the image forming operation as the correction mode. This is first performed in order to measure the difference in A / D value at the same input (input from the surface potential meter 273K) in each A / D converter 276K, 276Y. When receiving the instruction, in S301, the slave CPU 704 operates the input of the switch 274 so as to select the signal line 716. When the selection operation of the switch 274 is completed, in S102, the sub-master CPU 701 sends a setting instruction to the slave CPU 702 so that the drum surface potential of the photoconductor 225K becomes 500V. The drum surface potential can be set in a range from about 100 V to about 900 V. For example, an intermediate potential of 500 V is selected.

  Next, in S201, the slave CPU 702 instructs rotation control of the photosensitive member 225K and sets 500 V for the primary charging device 221K. Further, in S202, the slave CPU 702 detects the signal value from the surface potential meter 273K when the surface potential is 500 V by the A / D converter 276K. In parallel with S202, in S302, the slave CPU 704 uses the A / D converter 276Y to detect the signal value from the surface electrometer 273K when the surface potential is 500 V, similar to the A / D converter 276K. This is because the signal line 716 is connected under the control of the switch 274 in S301. Further, in S203 and S303, the slave CPU 702 and the slave CPU 704 send the detection value (A / D value) to the sub-master CPU 701.

  Next, in S103, the sub master CPU 701 compares the detection values sent from the slave CPU 702 and the slave CPU 704, calculates the difference, and notifies the slave CPU 704 of the difference. Here, the sub master CPU 701 is an example of a calculation unit. The difference is calculated by comparing digital data output from other A / D converters with the reference value using digital data output from any one A / D converter as a reference value. The In S304, the slave CPU 704 stores the sent difference value as correction data. On the other hand, in S104, the sub master CPU 701 notifies the slave CPU 704 of the input of the switch 274 to select the 717 signal line. In step S305, the slave CPU 704 controls the switch 274 based on the notified content. This is performed to change the input to the A / D converter 276Y to the output from the surface electrometer 273Y before shifting from the correction mode to the normal measurement mode.

  Finally, in S105, the sub master CPU 701 notifies the slave CPUs 702 and 704 of the transition from the correction mode to the normal measurement mode. Here, the slave CPUs 702 and 704 shift from the correction mode to the normal measurement mode. That is, the value detected by the reference A / D converter 276K is used as a reference value, and the difference from the value detected by the A / D converter 276Y is corrected during normal detection. Therefore, when normal detection is started, the slave CPU 704 functions as a correction unit and corrects the A / D value from the A / D converter 276Y using the correction data stored in the correction mode.

  In the above example, offset correction at one point at 500 V has been described. However, it is possible to further improve the accuracy of correction data from correction values of two or more points using a similar correction algorithm. In FIG. 8, the horizontal axis represents the surface potential, and the vertical axis represents the A / D value from the A / D converter. For example, the sub master CPU 701 functions as a first derivation unit, and determines the charging voltage value and each value from the value of the A / D converter 276K and the value of the A / D converter 276Y when the drum surface potential is at the lower limit 100V and the upper limit 900V. A relational expression indicating a relation with the difference in the charging voltage value may be derived. In this case, the slave CPU 704 stores the relational expression as correction data. Thus, storing the relational expression as correction data leads to further improvement in measurement accuracy.

  As described above, in the image forming apparatus according to the present embodiment, in the correction mode, each switch is controlled so that the output from the same surface electrometer is input to each A / D converter. The difference between the digital data output from the A / D converter is calculated. Further, in the normal measurement mode, the image forming apparatus corrects the output from each A / D converter so as to eliminate the difference calculated in the correction mode. As a result, the image forming apparatus can perform each control without using disadvantageous methods such as improving the accuracy of the reference power supply, increasing the functionality of the CPU chip, and increasing the accuracy in distributed control using a plurality of CPUs. The error of each A / D converter due to the difference in the reference potential in the CPU can be eliminated. In the above-described embodiment, the surface electrometer is described as an example of the output unit. However, for example, A / D conversion such as a detection value of a high voltage current / voltage, a detection value of a temperature of a fixing device, and other sensor detection values. Needless to say, the present invention can be applied to a system in which an analog signal is detected via a detector.

<Second Embodiment>
Next, a second embodiment will be described with reference to FIGS. 9 to 11. In the present embodiment, similarly to the first embodiment, the sub-master CPU 701, the slave CPU 702, and the slave CPU 704 in which the board configuration is separated in the image forming module 282 will be described as an example. In addition, about the structure similar to 1st Embodiment, the same reference number is attached | subjected and description is abbreviate | omitted. FIG. 9 shows the connection status of the sub-master CPU 701, slave CPU 702, and slave CPU 704 according to the second embodiment. FIG. 10 shows a part of the processing procedure of the image forming module 282 according to the second embodiment. FIG. 11 shows the relationship between the in-device temperature and the A / D value according to the second embodiment.

  First, each element will be described with reference to FIG. In the present embodiment, a temperature sensor 275 is provided in addition to the configuration of FIG. The temperature sensor 275 is provided in a place that is arranged in the image forming unit 300 and well reflects the ambient temperature of each substrate. Further, the temperature sensor 275 is input to the sub master CPU 701 via the signal line 719. As a result, the sub master CPU 701 can recognize the temperature data sequentially.

  Next, the operation of the second embodiment will be described with reference to FIGS. In the flowchart of FIG. 10, temperature measurement using the temperature sensor 275 is added before the execution of S101 by the sub-master CPU 701 from the flowchart of FIG. The numbers starting with S described below indicate step numbers in the flowchart. In FIG. 11, the horizontal axis represents temperature, and the vertical axis represents A / D value correction data. In the following, an example in which the low temperature value is preset to 0 degrees and the high temperature value is preset to 50 degrees as the temperature range acquired by the temperature sensor 275 is shown. These set values are examples, and can be changed according to the installation status of the image forming apparatus 1000.

  First, in S111, the sub master CPU 701 acquires the temperature measured by the temperature sensor 275. Subsequently, in S <b> 112, the sub master CPU 701 determines whether or not the image forming apparatus 1000 is a startup process in a predetermined time zone. Here, the predetermined time zone indicates a time zone such as in the morning when the image forming apparatus 1000 is in a relatively low temperature state. The predetermined time period can be changed according to the outside temperature of the installation location. If it is determined in S112 that it is the predetermined time zone, the sub-master CPU 701 proceeds to S113 and stores the detected value acquired from the temperature sensor 275 as a low temperature value. Thereafter, the same processing as in the flowchart of FIG. 6 is performed. However, in S103, the sub-master CPU 701 calculates correction data of the A / D converter 276Y from the difference between each A / D value and the acquired temperature value, and sends it to the slave CPU 704. Therefore, in S304, the slave CPU 704 stores the sent correction data. The correction data here is, for example, correction data at a low temperature value close to 0 degrees shown in FIG.

  On the other hand, if it is determined in S112 that it is not the predetermined time zone, the process proceeds to S114, and the sub-master CPU 701 determines whether or not low-temperature value correction data exists. If there is no low-temperature value correction data, the process proceeds to S115, and the sub-master CPU 701 stores the detected value acquired from the temperature sensor 275 as a low-temperature value. Thereafter, processing similar to the processing after S113 described above is performed. The correction data here is, for example, correction data at a low temperature value close to 0 degrees shown in FIG.

  On the other hand, if low temperature correction data exists in S114, the process proceeds to S116, and the sub-master CPU 701 determines whether or not the detected value is equal to or lower than the currently set low temperature. When the detected value is equal to or lower than the low temperature, the process proceeds to S117, and the sub master CPU 701 updates the detected value acquired from the temperature sensor 275 as the low temperature value. Thereafter, processing similar to the processing after S113 described above is performed. However, the correction data here is, for example, correction data at a low temperature value lower than 0 degrees shown in FIG.

  On the other hand, if the detected value is higher than the low temperature in S116, the process proceeds to S118, and the sub master CPU 701 determines whether correction data at the high temperature exists. When the correction data for the high temperature value does not exist, the process proceeds to S119, and the sub master CPU 701 stores the detection value acquired from the temperature sensor 275 as the high temperature value. Thereafter, processing similar to the processing after S113 described above is performed. However, the correction data here is, for example, correction data at a high temperature value close to 50 degrees shown in FIG.

  On the other hand, if the correction data for the high temperature value exists in S118, the process proceeds to S120, and the sub master CPU 701 determines whether or not the detected value is equal to or higher than the currently set high temperature temperature. When the detected value is equal to or higher than the high temperature, the process proceeds to S121, and the sub master CPU 701 stores the detected value acquired from the temperature sensor 275 as the high temperature value. Thereafter, processing similar to the processing after S113 described above is performed. However, the correction data here is, for example, correction data at a high temperature value higher than 50 degrees shown in FIG.

  As described above, in the present embodiment, the correction data is calculated from two or more points of the low temperature value and the high temperature value in the image forming apparatus. As described above, the sub master CPU 701 functions as a second derivation unit, derives a relational expression between the correction data and the temperature value, and can easily calculate the correction data at each temperature based on the relational expression. That is, when the relational expression is derived, correction data based on the detection acquired from the temperature sensor 275 using the relational expression can be calculated in step S103. In the above-described embodiment, offset correction at one point at 500 V has been described. However, it is possible to further improve the accuracy of correction data from correction values of two or more points using a similar correction algorithm.

Claims (5)

A plurality of output units for outputting analog data;
A plurality of analog-digital converters connected to any of the output units and converting analog data into digital data;
At least one switching unit that is provided between the output unit and the analog-digital converter and switches the output unit to which the analog-digital converter is connected;
In a state where the switching unit is controlled so that the output from the same output unit is input to each analog-digital converter, each digital data output from each analog-digital converter is eliminated by An image forming apparatus comprising: a correction unit that corrects an output from the analog-digital converter.   The image forming apparatus according to claim 1, further comprising a calculation unit configured to calculate the difference between digital data output from each analog-digital converter.   The calculation unit calculates a difference between the digital data output from the other analog-digital converter and the reference value using the digital data output from any one of the analog-digital converters as a reference value. The image forming apparatus according to claim 2. The output unit is a surface potentiometer that measures the surface potential of the image carrier,
The calculation unit calculates a difference between outputs from each analog-digital converter in a plurality of charging voltage values to the image carrier, and derives a relational expression indicating a relationship between the charging voltage value and the difference. 1 deriving section,
The image forming apparatus according to claim 2, wherein the correction unit corrects an output from each analog-digital converter using the relational expression derived by the first deriving unit. A temperature sensor for measuring the temperature in the image forming apparatus;
The calculation unit includes a second derivation unit that calculates the difference using a plurality of temperature values measured by the temperature sensor and derives a relational expression indicating a relationship between the temperature value and the difference,
The correction unit corrects the output from each analog-digital converter based on the temperature measured by the temperature sensor, using the relational expression derived by the second deriving unit. The image forming apparatus according to any one of 2 to 4.

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